The present invention relates to a telephone, and more particularly to such a telephone that allows handset and hand-free functions to be simultaneously operated.
A regular telephone, as shown in FIG. 1, comprises a keyboard 100 having a set of function buttons (not shown). The keyboard 100 is connected to a CPU 110. The CPU 110 is connected to ringing circuits 120, and connected to the respective input ends of first and second switches (K2,K3) 150 and 160. The first and second switches (K2,K3) 150 and 160 control a respective telephone line (LINE1, LINE2) 130 and 140. The first contact at the output end of the first switch 150 and the second contact at the output end of the second switch 160 are respectively connected to a third switch (K5) 190. The third switch 190 controls a talking circuit 170 and a hand-free circuit 180. The second contact at the output end of the first switch 150 and the first contact at the output end of the second switch 160 are connected to a fourth switch (K4) 200 at a load-circuit. The third and fourth switches 190 and 200 are respectively connected to the CPU 110. When a call comes through the first telephone line 130, the CPU 110 is triggered to output a control signal SWCTL1 to the first and second switches 150 and 160, causing the first and second switches 150 and 160 to be turned to high potential and the input end of each of the first and second switches 150 and 160 to be respectively connected to the first contact at the respective output end, therefore the first telephone line 130 is connected to the talking circuit 170 or hand-free circuit 180 through the third switch 190, and at the same time the second telephone line 140 is connected to the load-circuit, which is at an open circuit status. When two calls come through the first telephone line 130 and the second telephone line 140, the button HOLD at the keyboard 100 is depressed to close the fourth switch 200 at the load-circuit, enabling the telephone lines 130 and 140 to be maintained in communication, thus one of the telephone lines 130 and 140 can be selected by depressing button LINE1 or button LINE2 at the keyboard 100. If the first telephone line 130 is selected, the first, second, third and fourth switches 150, 160, 170 and 180 are maintained connected to the first telephone line 130. If the second telephone line 140 is selected, the first and second switches 150 and 160 are connected to the respective second contacts, causing the first telephone line 130 to be held, and the second telephone line 140 to be connected to the talking circuit 170 or hand-free circuit 180 through the third switch 190. Although the first and second telephone lines 130 and 140 can be simultaneously connected, the called party can only use the talking circuit 170 or hand-free circuit 180 to talk to the calling party at one telephone lines 130 or 140. For example, when two persons simultaneously made a call, one call is picked up through the handset (or hand-free circuit), and the other call is held by means of the operation of the button HOLD. Through buttons LINE1 and LINE2, either call is selected. This design of telephone allows two calls to be received through the first and second telephone lines 130 and 140, however one call must be held on the line while the other is picked up through the handset or hand-free circuit.